Brake pads are known to be used in brake systems. For example, brake pads are used to contact brake discs, or other moving components, to decrease or prevent the motion of a motor vehicle. This is usually performed by using a calliper apparatus to press the brake pad onto the moving component. Conventionally, brake pads have a surface area which engages a surface of the moving component. A coefficient of friction across the brake pad determines the frictional force that the brake pad can supply to stop the motion of the component. It is desirable to have a high coefficient of friction of the brake disc to provide good braking power. Therefore, brake pads generally have a constant coefficient of friction across the surface.
Brake pads such as those mentioned above provide adequate stopping ability but are susceptible to instabilities on contact with the moving component. The instabilities can result in undesirable effects such as wear, heat generation and brake noise. Methods of reducing such instabilities are known. For example, a shim may be provided behind the brake pad relative to the surface facing the brake disc, which is designed to dampen the instabilities. Nevertheless, brake squeal still remains to be a problem.
DE4140220 describes a brake pad having a coefficient of friction that varies across the brake pad. The area of the brake pad proximal to a rotation axis of a brake disc has a high coefficient of friction. Accordingly DE4140220 aims to provide a brake pad that, on contact with the brake disc, heats up evenly across its surface and therefore decreases turbulence. However, the brake pad of DE4140220 still suffers from instabilities that cause brake squeal. Furthermore, the brake pad of DE4140220 may lead to a loss in braking power when compared to a brake pad having a constant coefficient of friction across the surface.
JP2005-299841 describes a brake pad that aims to reduce brake squeal by providing a brake pad comprising two materials, one having a high coefficient of friction and the other having a low coefficient of friction. The material having the low coefficient of friction is positioned proximal to a rotation axis of a brake disc. A calliper supplies a force to press the region of high coefficient of friction onto the brake disc. The region of high coefficient material is formed radially thin, i.e. having a small area, in comparison to the region of low coefficient material, which is radially thick and therefore has a large area. JP2005-299841 purports that brake squeal is reduced by this configuration. However, in the event that the relatively large area of low coefficient material contributes to the stopping ability of the brake pad, the large area of low coefficient material is susceptible to produce brake squeal. Therefore, the brake pad of JP2005-299841 either suffers from brake squeal or reduced stopping ability, both of which are undesirable.
It is therefore an object of the present invention to ameliorate the aforementioned problems.